Once the website is initially loaded with a given value for any of these two parameters, the framework in the front-end will always append these values to all subsequent requests. In the image below, themestyle=expansive is added to all requested URL, either as a link clicked upon by the user, or dynamic content fetched by some component:

Then, a PoP site can be customized using these parameters, and users can be served either version. Because this information will always be in the requested URL, then we can analyze and measure the impacts of each design very easily. Finally, to append one or another parameter value to the URL, the URL is intercepted in the client through Service Workers, adding a parameter or the other following the weight given to each.